XML-Linking

1
XML-Linking

• XPath, XPointer
• XLink
• XSL (a taste)

2
HTML linking

• Trivial syntax
• lta href"http//foo.net/x.html"gt
• Trivial to implement
• Some ability to go to specific targets (ID only)
• lta href"http//foo.net/x.htmlsec2"gt
• Embedded markup lets source anchors move with
  editing
• (unlike, say, byte offsets)

3
HTML linking limitations

• 1 Two elements A and IMG
• 2 One link behavior for A, one for IMG
• 3 No real link type system
• 4 URLs as pointing mechanism
• 5 Privileged end lives inline in origin document
• 6 Destination is a whole document
• 7 One destination No aggregate destinations
• 8 One way A or IMG to somewhere

4
A family of technologies
XML
Structuring Documents
5
Linking in XML

• Needs to overcome three things
• How do I address an anchor point in both the
  SOURCE node and the TARGET node (rather than a
  whole target resource with a Uniform Resource
  Identifier) ?
• How do I introduce link types?
• How do I manage external/multi-ended links?

6
XPointer

• Provides addressing into XML document structure
  attaching the links end(s)

d
o
c
t
i
t
l
e
d
e
s
c
r
i
p
A pointer identifies a point, node, or range in
a document
s
t
a
t
u
s
t
r
e
v
i
s
i
o
n
c
o
d
e
c
o
d
e
7
XLink

• Provides the connection where/what is the line
  between?
• add behaviors to links
• without using Javascript

A link groups data portions anddescribes their
relationships
8
URLs as pointers

• Very prone to breakage
• Fundamentally point to copies, not objects
• Like a bibliography that cites shelf position
  instead of author, title, and date
• URLs presume retrieving whole documents
• Therefore, people break non-trivial documents
  into bits
• But, since theres no typing, you cant tell
  which links mean reassemble
• Therefore, indexers cant reassemble or detect
  whole documents, just pages
• Therefore, you cant have automatic assemble and
  retrieve/print/search
• Guess why theres not very much literature on the
  Web?

9
Addressing in HTML

• ltpgtFor information about the XPointer language
  that lta title"Must, May, etc."
  href"dt-must"gtmaylt/agt be used with XLink, see
  lta href"xptr"gtXPTRlt/agt.lt/pgt
• ltdt class"label"gtlta name"xptr"gtlt/agtXPTRlt/dtgtltddgt
  Ron Daniel, Steve DeRose, and Eve Maler,
  editors.ltcitegt XML Pointer Language (XPointer)
  V1.0lt/citegt. Metacode Technologies, Brown
  University, and Sun Microsystems.
• Burlington, Seekonk, et al. World Wide Web
  Consortium, 1998. (See lta href"http//www.w3.org
  /TR/xptr"gthttp//www.w3.org/TR/xptrlt/agt.)lt/ddgt

10
Addressing in XML

• ltmessagesgt
• ltnote ID"501"gt
• lttogtTovelt/togt
• ltfromgtJanilt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtDon't forget me this weekend!lt/bodygt
• lt/notegt
• ltnote ID"502"gt
• lttogtJanilt/togt
• ltfromgtTovelt/fromgt
• ltheadinggtRe Reminderlt/headinggt
• ltbodygtI will not!lt/bodygt
• lt/notegt
• lt/messagesgt

Addressing elements (like the note element)
http//www.ex.org/mgesid(501)
11
Destination is a whole document

• Exception can scroll to ID if it existsltA
  HREF"http//xyz.com/foo.htmlid(37)"gt
• No way to point to anything but an element
• Author controls what others can reference
• Imagine on paper You can only quote or footnote
  paragraphs 1, 12, 17, or 20.
• Since documents are fragmented to make pages,
  the whole document isnt anyway
• You cant link to a whole play/novel/etc on the
  Web, since it wont be there as a whole (or if it
  is, you cant read it feasibly with browsers)

12
XPath and XPointer

• How do I address an anchor point in both the
  SOURCE node and the TARGET node?
• XPath
• Expression language that addresses parts of an
  XML document
• Basic facilities for string, number and boolean
  manipulation
• Operates on the abstract, logical tree structure
  of an XML document
• Uses the XML regular structure as guideposts in
  the expressions
• Gets its name from the use of a path notation
  navigating through the hierarchical structure of
  an XML document
• BUT it only addresses XML nodes (elements,
  attributes, text).
• XPointer
• Addresses freely any fragments of an XML document
• Spans across XML chunks

13
XPath Components (1)

• An XPath expression operates over
• CONTEXTS to create NODE
  SETS

root
/
book

abstract
title
chapter
chapter
chapter
ID 'intro'
ID'summary'
ID'concepts'
section
section
para
title
para
para
Attribute
list
...
ID'p37'
a
xref
Element
namecarole'
href'id(intro)'
14
XPath Components (2)

• The context for an XPath expression is the node
  in the source XML document currently being
  processed.
• E.g. "/", means that we are in the context of the
  root of the XML document.
• The location path sets the context of the node
  that you're trying to find.
• A location path expression is an expression used
  for selecting a node set by following a path of
  locations steps.
• Each location step is made up of the combination
  of
• an axis
• a node test
• zero or more predicates

15
XPath Components (3)

• An axis returns a list of nodes, based on the
  context of the original node, corresponding to
  the relationships in ordered trees
• E.g. child axis locates the set of all the
  current context node direct sub elements.
• A node test specifies the type of a node,
  including general types like comment() or
  specific types
• E.g. childbook, selects all the book elements
  that are children of the current context node
• A predicate filters the node list located by the
  axis and the node-test
• E.g. childselfauthor or selfreviewer
• selects all children of the current node that are
  either of element type author or reviewer
• Childchapterchildabstract selects chapter
  children of the context node that have abstracts

16
XPath Components (4)

• Expressions return a node-set selected by the
  operators, path locations and filters used in the
  XPath expression.
• chapterauthor"Jones" or author"Scott"
• returns chapter nodes where the author is Jones
  or Scott

17
XPath Examples

• childpara selects the para element children
• child selects the element children
• /descendantpara all the para elements of the
  document
• /book/chapter5/section2 the second section of
  the fifth chapter of the book elements under the
  document root
• /descendantpposition()last() the last p in
  document order
• //note_at_type"warning" all note elements that
  has a type attribute with value warning

18
XPointer Usage

• How do I address an arbitrary anchor point in the
  node?
• XPointer is the fragment identifier portion of
  any URI reference. So it encapsulates an XPath
  expression in a URI reference .
• Could be bare names just like html
• Intro
• Or could embed the expression
• xpointer(id(intro))

19
XPointer extensions to XPath

• Initialization of the XPath context
• XPath Node concept is extended to a location
  node, point or range
• A location-set is a generalization of XPath's
  node-set
• XPointer generates an ordered list of nodes,
  points or ranges within the document, not just
  nodes (like XPath did)

20
XPointer Examples

• xpointer(//local-name()'y' and
  namespace-uri()'http//www.foo.com/bar')
• locates all the y elements from the namespace
  whose URI is http//www.foo.com/bar
• xpointer(id("sec2.1")//p2 range_to
  id("sec2.2")//plast())
• selects the range from the second p child of
  sec2.1 to the end of the last p in sec2.2
• string-range(//title,"XPointer")
• returns the set of ranges containing "XPointer"
  strings when they occur within title elements

21
XPointer

• locate the range from the start-point for the
  element with ID "chap1" to the end-point for the
  element with ID"chap2".
• xpointer(id("chap1")/range-to(id("chap2")))
• select, for each revision, a range starting at
  the beginning of the REVST element and ending at
  the end of the next REVEND element
• pointer(descendantREVST/range-to(followingREVE
  ND1))

22
XPointer extensions to XPath

• A string-range() function to address within node
  content
• The functions start-point() and end-point() to
  address beginning and ending of locations.
• The unique() function to detect absence or
  multiple return values.
• The functions here() and origin() to refer to the
  XPointer expression location and hypertext
  traversal

23
The here() function example

• here function appears inside an XPointer that is
  in an attribute node. The XPointer as a whole
  returns the slide element just preceding the
  slide element that most directly contains the
  attribute node in question.
• ltbutton
• xlinktype"simple
• xlinkhref"xpointer(here()/ancestorslide1/pr
  ecedingslide1)"gt
• Previous
• lt/buttongt

24
XPointer Summary

• So, extensions to XPath allow XPointer to
• Address points and ranges as well as whole nodes
• Locate information by string matching
• Use addressing expressions in URI references as
  fragment identifiers
• Extends XPath types and add specific operations

25
Linking in XML

• Needs to overcome three things
• How do I address an anchor point in the SOURCE
  and TARGET node (rather than a whole target
  resource with a Uniform Resource Identifier) ?
• How do I introduce link types?
• How do I manage external/multi-ended links or
  more generally, how do I control link behaviour?

?
26
XLink Linking Model (1)

• XLink a way to gather locations to make links
• Link elements (anchors)
• Element being connected by a link
• Locator
• Addresses remote resource
• Arc
• Information about how to traverse a pair of
  resources, including the direction of traversal
  and possibly application behavior
• Link
• Aggregates the above into a set of a given
  link-type.
• May include multiple locators and arcs to present
  multi-ended links.

27
XML Link Model (2)

• Remote resources
• If the resource is addressed by its URI reference
• I.e. specified by reference
• Local resource
• If the resource participates in the link by
  virtue of being a link element or its parent
  being a link element
• Specified by value

• Outbound links
• Local start, remote end
• Inbound links
• Remote start, local end
• Third party
• Remote start, remote end
• Linkbases
• Documents containing collections of inbound and
  third-party links

28
XLink Simple Example

• ltmycrossReference
• xmlnsmy"http//example.com/"
• xmlnsxlink"http//www.w3.org/1999/xlink"
• xlinktype"simple"
• xlinkhref"students.xml"
• xlinkrole"studentlist"
• xlinktitle"Student List"
• xlinkshow"new"
• xlinkactuate"onRequest"gt
• Current List of Students
• lt/mycrossReferencegt

Link type
Link location
Link metadata
Link traversal behaviour
29
XLink Identifying link elements

• linking element, which is an XLink-conforming XML
  element that asserts the existence of a link.
• There are two types of linking element
• Simple
• Extended
• Four types of link metadata elements
• Arc
• Locator
• Title
• Resource

30
XLink Elements

• Simple Links
• an outbound link with exactly two participating
  resources (just like HTML-style A and IMG links
  fall). Little functionality, no special internal
  structure.
• Extended links offer full XLink functionality,
• such as inbound and third-party arcs
• links that have arbitrary numbers of
  participating resources
• Their structure can be fairly complex, including
  elements for
• Pointing to remote resources,
• Containing local resources,
• Specifying arc traversal rules,
• Specifying human-readable resource and arc titles
• special ways of finding linkbases

Locator to remote resource
Locator to remote resource
Locator to remote resource
extended
Local resource
Locator to remote resource
Locator to remote resource
31
Extended Links

• Containers for explicit locators and arc
  subelements
• Traversal rules govern directionality and
  behaviour
• Locator attributes
• href - XPointer
• Semantic attributes
• Role a property the entire link has
• Arcrole a property the arc has
• Title human readable description of the entire
  link
• Traversal Attributes
• Label a way for an arc to refer to the link
• From labelled source of the link
• To labelled the destination of the link
• Link behaviours
• Show - replace, new, embed, other, none
• Actuate onLoad, onRequest, other, none

32
Example

• ltcourseloadgt xlinktypeextended"
• lttooltipgtxlinktypetitle Course Load for Pat
  Joneslt/tooltipgt
• ltperson
• xlinktypelocator"
• xlinkhref"students/patjones62.xml"
• xlinklabel"student62
• xlinkrole"http//www.example.com/linkprops/s
  tudent
• xlinktitlePat Jones /gt
• ltcourse
• xlinktypelocator"
• xlinkhref"courses/cs101.xml"
• xlinklabel"CS-101"
• xlinktitle"Computer Science 101" /gt
• ltgpa xlinktyperesource xlinklabel"PatJonesG
  PA"gt3.5lt/gpagt
• ltgo
• xlinktypearc"
• xlinkfrom"student62"
• xlinkto"PatJonesGPA"
• xlinkshowreplace"

Link type
Link metadata
Link location
Traversal attributes
Link traversal behaviour
33
XML-Linking goals end user

• Dynamic updates and patches
• Push updates without re-sending whole docs
• Highlighter annotations
• Shareable annotations
• Links from un-writable documents
• Which is most of the Web, for any person
• Large sets of managed links
• An entirely new market for links per se
• Anyone can sell their commentary on other data

34
XML Linkbases

• lt!ELEMENT basesloaded ((startrsrclinkbaseload))
  gt
• lt!ATTLIST basesloaded
• xlinktype (extended) FIXED "extended"gt
• lt!ELEMENT startrsrc EMPTYgt
• lt!ATTLIST startrsrc
• xlinktype (locator) FIXED "locator"
• xlinkhref CDATA REQUIRED
• xlinklabel NMTOKEN IMPLIEDgt
• lt!ELEMENT linkbase EMPTYgt
• lt!ATTLIST linkbase
• xlinktype (locator) FIXED "locator"
• xlinkhref CDATA REQUIRED
• xlinklabel NMTOKEN IMPLIEDgt
• lt!ELEMENT load EMPTYgt
• lt!ATTLIST go
• xlinktype (arc) FIXED "arc"
• xlinkarcrole CDATA FIXED
  "http//www.w3.org/1999/xlink/properties/linkbase"
  
• xlinkactuate (onLoadonRequestothernone)
  IMPLIED
• xlinkfrom NMTOKEN IMPLIED

• ltbasesloadedgt
• ltstartrsrc xlinklabel"spec"
  xlinkhref"spec.xml" /gt
• ltlinkbase xlinklabel"linkbase"
  xlinkhref"linkbase.xml" /gt
• ltload xlinkfrom"spec" xlinkto"linkbase"
  actuate"onLoad" /gt
• lt/basesloadedgt

35
Processing XML

• An XML file only has
• data semantics
• The remainder
• presentation semantics
• user interface semantics
• behavioural semantics
• must be mapped on somehow.
• Processing XML
• High level - XSL
• Medium Level - DOM / JavaScript
• Low Level - SAX / Java

• XSL is a language that can
• transform XML into HTML,
• filter and sort XML data,
• address parts of an XML document,
• format XML data based on the data value
• output XML data to different devices, like screen
  or voice

36
XSL - The Style Sheet of XML

• XSL provides
• an XML vocabulary for specifying formatting
  semantics
• a language for transforming XML data
• XSL consists of three parts
• a language for transforming XML documents XSLT
• a language for defining XML parts and patterns
  XPath
• a language for formatting XML documents
  Formatting Objects DTD
• XSL uses
• templates
• match an element in the original document
• specify the new content to replace the element by
• specify the template matches using XPath

37
XSL Processing
Web page
Printed document
mydoc .xml
mydoc .dtd
WAP page
style .xsl
XSLT processor
XSL processor
FOdoc .xml
FO .dtd
FO .xsl
38
XML-gtXSL-gtpretty picture

• lt?xml version'1.0'?gt ltxslstylesheet
  xmlnsxsl"http//www.w3.org/TR/WD-xsl"gt
• ltxsltemplate match"/"gt
• lthtmlgt ltbodygt
• lttable border"1"gt lttrgt
• ltthgtTitlelt/thgt
• ltthgtArtistlt/thgt lt/trgt
• lttrgt lttdgt
• ltxslvalue-of select"CATALOG/CD/TITLE"/gtlt/tdgt
  lttdgt
• ltxslvalue-of select"CATALOG/CD/ARTIST"/gtlt/tdgt
  lt/trgt lt/tablegt lt/bodygt lt/htmlgt
• lt/xsltemplategt
• lt/xslstylesheetgt

• lt?xml version"1.0"?gt
• lt?xml-stylesheet type"text/xsl"
  href"cd_catalog.xsl"?gt
• ltCATALOGgt
• ltCDgt
• ltTITLEgtEmpire Burlesquelt/TITLEgt
• ltARTISTgtBob Dylanlt/ARTISTgt
• ltCOUNTRYgtUSAlt/COUNTRYgt
• ltCOMPANYgtColumbialt/COMPANYgt
• ltPRICEgt10.90lt/PRICEgt
• ltYEARgt1985lt/YEARgt
• lt/CDgt
• .
• lt/CATALOGgt

39
Further Reading Tutorials

• www.W3Schools.com
• www.zvon.org
• www.xml.com